Schizencephaly

Two types of schizencephaly are recognized: a "closed-lip" schizencephaly in which the cleft walls are contiguous and an"open-lip" schizencephaly in which the walls are separated by wide subarachnoid spaces.

The grey matter lining the cleft is usually polymicrogyric (see polymicrogyria). The clefts can be unilateral or bilateral, symmetrical or asymmetrical and can appear anywhere in the brain. These lesions are believed to be due to in utero vascular injuries and their preferential location in the perisylvian areas follows the frontoparietal distribution of the middle cerebral artery.

The clinical condition of patients relates to the amount and location of involved brain: patients with a narrow, unilateral cleft usually present with seizures and mild focal neurological deficits and they are otherwise developmentally normal; patients with bilateral clefts often have severe developmental delay with early intractable epilepsy and severe motor dysfunction.

On imaging studies the key feature in the diagnosis of any type of schizencephaly is the presence of a ventricular dimple at the ependymal surface of the cleft. This can be the only CT feature in cases of closed or minimally open lip schizencephaly. On MR images the thickness of the transhemispheric cleft and the polymicrogyric aspect of the grey matter lining the cleft are better discernible (Fig.1). Heterotopic grey matter lines the ventricle adjacent to the cleft in more than half of cases. Associated anomalies include: mild hypoplasia of the corpus callosum, and total or nearly total absence of septum pellucidum (7090% of affected patients) which is found in association with optic nerve hypoplasia on clinical examination in 3050% of patients (defined to have septo-optic dysplasia with schizencephaly). The optic nerves should always be investigated by clinical examination and MR study in these patients, especially when visual symptoms are present.

In patients with open-lip schizencephaly, CSF pulsations from the lateral ventricles may produce scalloping of the inner table of the skull. Plagiocephaly may occur occasionally in the most severe cases requiring ventriculoperitoneal shunt.

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